1. Field of the Present Invention
The present invention generally pertains to devices and methods for measuring the geometric characteristics of terrain. More specifically, the present invention uses a wheeled instrument with a sensor array to trace the profile of a land surface.
2. Description of the Related Art
The manually operated Measuring Wheel is a classic tool of the surveyor""s art and is often used in conjunction with other measuring instruments to produce a geometric representation of the terrain. The use of this device is generally a time consuming and expensive process which requires a highly trained individual.
Typically, this instrument is a pole with an affixed handle at one end and a supporting wheel at the other. The supporting wheel is equipped with an odometer that is either mechanical (U.S. Pat. No. 275,734) or electronic (U.S. Pat. No. 4,409,663).
Methods have been developed for automatic surveying of very large plots of land using motorized land vehicles, such as disclosed in U.S. Pat. No. 5,174,038, or aircraft, such as disclosed in U.S. Pat. No. 5,557,397, which naturally require very expensive equipment and highly skilled operators. Such large-scale systems may depend on satellites; say via GPS or DGPS (U.S. Pat. No. 5,999,878) or photogrametry (U.S. Pat. No. 5,517,419).
Small scale automated surveying systems, such as disclosed in U.S. Pat. No. 5,956,660 or German patent DE 19729355 (based on inertial dead reckoning) are subject to error accumulation, and so have limited practical value.
A useful addition to the Measuring Wheel would be the ability to make and keep a digital record of its track. A precise track would allow the Measuring Wheel to function as a stand-alone surveying device. Several attempts have been made in this direction:
German patent DE4036424 discloses a three-wheeled device designed for flat terrain. The device contains two coaxial measuring wheels, which is sufficient to determine the contour of travel in the plane of motion of the device, subject to the usual error accumulation problem. Since any discrepancy between the odometry of the two wheels is interpreted as a change in orientation, the operator will be required to take care that neither wheel slips during turns, which will make the device considerably more difficult to use than a standard Measuring Wheel. A related patent, DE4115809, teaches that, with the addition of an inclinometer along its forward axis, that device would have the capability to measure changes in elevation as well, but this will only be accurate if the device moves directly up or down hill.
Another attempt to measure contours is disclosed in German patent DE3925133, which, instead of a wheel, uses a ball that is able to roll in any direction on the surface to be surveyed. During its motion, this ball must maintain physical contact with the balls of two computer mice that are affixed to the housing of the device. When this device is used outdoors dirt and moisture come in contact with the rolling ball and are transferred to the bearings and the mice. In a clean environment, the device will be affected by the usual error accumulation. Also, the operator is responsible for maintaining the housing at a level attitude while surveying.
World patent application WO9627779 discloses a method of profiling terrain with a device supported by at least one wheel equipped with an odometer, together with orientation sensors to determine the direction of the measurement wheel. For devices with a single supporting wheel, the track of a wheel on a surface depends on both the attitude of the wheel and the attitude of the surface. Even if the attitude of a wheel is sensed perfectly, without a method to determine the attitude of the surface on which it rests, an accurate track cannot be made. Distortion will be introduced in the track even when surveying terrain that is known a priori to be flat. Of the particular embodiments disclosed in this patent only the device disclosed in claim 17, in which the wheel is rigidly connected to two other supporting wheels, is not vulnerable to surface attitude distortion. This three wheeled device, however, lacks the freedom of movement of the traditional Measuring Wheel, making it awkward to use in an outdoor environment, and prone to inaccuracies resulting from the tendency of one or more of the of support wheels to lose contact with the surface over uneven terrain.
Accordingly, it is desirable to accurately track two- or three-dimensional contours with a device having fewer than three supporting wheels in which the guide-pole is able to tip from side to side as well as forwards and backwards, like a traditional Measuring Wheel.
The invention pertains to a device and method for accurately measuring geometrical features of terrain using a measurement wheel, orientation and heading sensors, and a computing device. The present invention enables the description of a two or three-dimensional landscape.
Accordingly, in one aspect of the present invention, a measurement device includes a wheel that is propelled by the operator using a guide-pole and handle, a sensor compartment rigidly mounted to the device, a digital odometry sensor (e.g., a digital odometer that measures the distance traveled by the wheel). Since the device is supported by one wheel only, the operator of this device has the same freedom of movement as has the operator of a classic Measuring Wheel.
The above aspect may also include a detachable computer with input and output peripherals, as well as a a sensor array for detecting the attitude of the wheel in space, or on a surface. Specifically, the attitude can be sensed by any method that yields a log of data from which the pitch, roll and yaw of the device may be recovered with respect to a fixed coordinate system. Accordingly, in the present invention the fixed coordinate system may be defined with respect to the earth or other convenient reference frame.
The present invention also provides for the extraction of a heading vector. The heading may be determined by any method that yields, from among the vectors in the plane of the measurement wheel, the vector which points in the direction of the instantaneous motion of the device.
The operator guides the measuring device over the terrain along the contour to be measured. The output of the digital odometer and other sensors are periodically recorded and combined in a sensor log, which is digitally stored on the hand-held computer. Since the attitude and heading of the measurement wheel are encoded in the sensor log, the data collected from the sensors may be processed, either in real time or later, and combined with the odometry to yield a discrete record of the track of the device, that is, of the locations through which the instrument has traveled relative to a fixed coordinate system.
In one embodiment, the sensor array comprises three sensors, said sensors being selected from the group consisting of accelerometers, inclinometers and magnetometers, or a combination thereof. In other embodiments, the sensor array is selected from the group consisting of two magnetometers and two accelerometers; two magnetometers and two inclinometer; two magnetometer and two gyroscopes; two accelerometer and two gyroscopes; and two inclinometers and two gyroscope.
Applications of such a device include, but are not limited to:
a. measuring the distance traveled by the Measuring Wheel. This is the same information available with the current generation of Measuring Wheels.
b. measuring the straight-line distance between two points when there are intervening obstacles. Ponds, fences, trees, houses, debris, etc. can be avoided and the device will still measure an accurate straight-line distance between two points.
c. measuring surface area. The digitization of the contour makes an estimate of the included surface area possible. This is especially useful for measuring irregular contours. For example, the device could measure the area of a curving driveway and effectively estimate the amount of asphalt needed to cover the surface.
d. measuring acreage. Since acreage of a region is computed from a two dimensional vertical projection, this device can accurately compute the acreage included in a contour, having applications in land development and management.
e. accident and crime scene reconstruction. The device can trace non-linear contours, e.g. tire marks on the road following an automobile accident, in much greater detail than existing Measuring Wheels. This facilitates a more accurate reconstruction of the event.
For a better understanding of the invention, reference is made to the below referenced drawings and written description following immediately hereafter.